Not wallpapered but painted RV walls. First prime and size the walls where ypu will be papering with a quality product like
Zinsser Shieldz. Use a quality adhesive like
Roman Adhesive to hang the paper. Be sure to have plenty of single edge razor blades on hand. A sharp blade is the key to a clean trim, and depending on the paper, sometimes you only get 1 or 2 good cuts with a fresh blade.
Wallpapering the RV is about the same as doing it in your home, lots of patience required for the process. One key difference is you start wallpaper at home by drawing a plumb line, that only works in the trailer if the unit is perfectly leveled when you park. Better idea is to line up with a door or cabinet frame.